WASHINGTON (Reuters) - In the rugged mountains of eastern Afghanistan, where the United States has already trimmed its forces ahead of the coming NATO withdrawal, a modest number of al Qaeda fighters have re-established operations, U.S. officials say, a worrying sign of the risks that could jeopardize Western hopes of a smooth exit.
Current and former U.S. officials say the fighters, believed to be mostly Arabs and Pakistanis who number less than 100, have crept back across the porous border with Pakistan to Kunar and Nuristan provinces. That is where a consolidation of NATO bases has left a force of just 4,200 Western soldiers - and a limited ability to conduct on-the-ground intelligence and security operations.
The reappearance, small as it may be, is emblematic of the challenges the Obama administration and its NATO allies will face as they seek to extricate themselves from a long and costly war without surrendering an unstable, still-violent Afghanistan back to militants intent on attacking the West.
"We're aware of attempts by al Qaeda to try and establish a presence in eastern Afghanistan, but ensuring they do not remains a focus of the campaign," a U.S. defense official said.
President Barack Obama, who drew a sharp contrast with Iraq when he called Afghanistan a 'war of necessity' for U.S. security, has defined the U.S. mission there largely as one of dismantling al Qaeda even as his soldiers continue to die at the hands of the Taliban.
That focus - rejecting a boundless campaign to defeat the Taliban or transform Afghanistan - has allowed Obama to project a measure of success there a year after he dispatched Navy SEALS to kill al Qaeda leader Osama bin Laden in Pakistan, and as he proceeds with plans to pull out most U.S. troops by the end of 2014.
But as Obama prepares to host NATO leaders for a May 20-21 Chicago summit, and his campaign to win a second term in November intensifies, success by other measures is far from assured.
While Obama's surge of 33,000 troops has weakened the Taliban in much of its southern heartland, the group remains able to recharge in Pakistan's tribal areas. Militants from the Haqqani network have embraced sophisticated attacks on Kabul.
Despite a Herculean aid effort that has cost the West billions of dollars, Afghanistan's ineffective institutions and widespread corruption make governance a weak link.
While U.S. officials see President Hamid Karzai as a questionable ally, it is even less clear what will follow after the 2014 elections in a country where former warlords still wield outsized power and political parties barely exist.
Obama is likely to use the Chicago summit to tout a new deal outlining a long-term U.S. presence in Afghanistan, which he signed in a middle-of-the-night visit to Kabul in early May.
But Washington has appeared to struggle in its effort to secure $1.3 billion a year from its allies to fund Afghan security forces, fueling doubts about how much support cash-strapped Western nations will be able to muster in the future.
The stakes could not be higher.
"No matter what happens in the coming years, it is pretty clear that the United States will remain prepared to act against any potential terrorist threats to U.S. homeland security that emerge in Afghanistan," said Brian Katulis, a senior fellow at the Center for American Progress in Washington. As in operations in Yemen, reliance on drones and special forces is expected.
"No matter who wins the election in November in the United States, future presidents will not risk a return to the situation the world saw in Afghanistan in the 1990s," he said.
The summit's U.S. hosts are sure to stress the NATO pledge of 'in together, out together,' a motto hearkening back to the early days of the war, when a Western coalition appalled by the September 11, 2001, attacks had not yet been strained by a Taliban military revival and by fiscal crisis and fatigue at home.
U.S. General John Allen, who commands U.S. and NATO forces in Afghanistan, will complete the removal of all Obama's surge troops this fall, leaving a U.S. force of about 68,000.
Allen is due to make recommendations for further troop reductions after the summer combat season, which should reveal how well Afghan forces can fight - and how well NATO fares with a force smaller than the one that claimed swathes of the Afghan South in a troop-heavy, counter-insurgency campaign in 2010.
But the victory of Socialist Francois Hollande in France, who has promised to pull French troops this year, raises questions. European nations are already anxiously watching for signs the Obama administration will accelerate its plans.
And there are fears, among Republicans and even some within the Pentagon, that the pace of remaining troop reductions will be determined by politics rather than conditions on the ground.
"To the extent we've had success it has involved large numbers of troops," a Republican congressional aide said.
NATO's strategy now hinges on success of its push to build up the inexperienced local army and police, an effort that has been a focus of U.S. investment since 2009, to mixed results.
Afghan forces number far more than they did, and their fighting skills are vastly improved. But their reliance on outside help for key tasks, such as intelligence and air support, will continue for years to come.
No one knows when Afghanistan will be able to pay for more than a small share of those security costs.
The good news, said Bruce Riedel, a former CIA official who chaired Obama's 2009 review of Afghan strategy, is Afghan forces need to be only skilled enough to keep the Taliban at bay.
"An Afghan stalemate with the Taliban is not the best outcome, but it is good enough since it keeps the Taliban out of Kabul and lets us use Afghan bases to carry out counter terror missions," in the region, Riedel said.
As the Pentagon seeks to stretch a shrinking force, military officials' frustration with Pakistan is palpable. Many U.S. officials see the ostensible ally, which they suspect of turning a blind eye to insurgents, as the chief threat to achieving their goals in Afghanistan. Pakistan denies such charges.
"There are things that are out of our control from a military perspective," one senior U.S. defense official said. "The safe haven element is huge."
As time goes on, the United States will focus its Afghan effort less on population security - the core of the counter-insurgency model credited with salvaging the war in Iraq - and more on targeted raids on militants and strikes from the air.
That is already the case in Kunar and Nuristan, where local officials warn that dozens to a few hundred non-Afghan militants have appeared, perhaps due to pressure on militants across the border in Pakistan. There is also a robust Taliban presence there.
Over the weekend, NATO aircraft struck targets in Kunar's Watapur district, killing four men suspected to be al Qaeda militants, U.S. officials said.
After U.S. forces shut a number of smaller bases in 2009-10 after taking heavy losses, the Taliban made advances in places like Nuristan's Wanat district. Given the small NATO presence, it will be largely up to some 23,000 Afghan police and army in the two provinces to face off against militants, including the Taliban, whose proximity to the border has allowed it to launch some of the largest assaults around Afghanistan.
"I'm disturbed by what I perceive as a real lack of understanding about what is possible in Afghanistan," said Robert Grenier, a former senior U.S. intelligence official who was CIA station chief in Pakistan until 2002.
"If we focus exclusively on counter-terrorism goals without maintaining a fairly robust counter-insurgency effort, we could see large parts of Afghanistan slip effectively into Taliban control. That makes me very concerned about the potential for long-term safe-havens," he said.
Additional reporting by Hamid Shalizi and Amie Ferris-Rotman in Kabul and Mark Hosenball in Washington; Editing by Warren Strobel and Jackie Frank